The primary emphasis in genetic modification has been directed to prokaryotes and mammalian cells. For a variety of reasons, plants have proven more intransigent than other eukaryotic cells to genetically manipulate. However, in many instances, it is desirable to effect transcription of an introduced nucleotide sequence of interest in a plant.
Expression of a heterologous DNA sequence in a plant is dependent, in part, upon the presence of an operably linked transcriptional control sequence, such as a promoter or enhancer, which is functional within the plant. The transcriptional control sequence determines when and where within the plant the heterologous DNA sequence is expressed. For example, where continuous expression is desired throughout the cells of a plant, constitutive promoters are utilized. In contrast, where gene expression in response to a stimulus is desired, an inducible promoter may be used. Where expression in specific tissues or organs is desired, a tissue-specific promoter may be used.
Accordingly, there is a substantial interest in identifying transcriptional control sequences, such as promoters or enhancers, which are active in plants.
Frequently, it is desirable to specifically or preferentially direct transcription in particular plant organs, tissues or cell types, or at particular developmental stages of the plant.
For example, the nutritional value of grain in cereal crop plants can be increased by genetic manipulation of the plant's genome with a seed-preferred promoter operably linked to a heterologous gene that encodes for the production of one or more nutrients. ‘Golden Rice’ provides a specific example of a plant with grain having an altered nutritional content (increased β-carotene) as a result of the grain-specific expression of a transgene (see Paine et al., Nature Biotechnology 23: 482-487, 2005).
Furthermore, expression of a toxic polypeptide (such as diphtheria toxin, barnase or the like) in male or female reproduction-associated plant parts of a plant may be used to effect male or female sterility in the plant.
Thus, isolation and characterization of transcriptional control sequences, which can serve as regulatory regions for the expression of heterologous nucleotide sequences of interest in reproduction-associated plant parts, such as seeds or anthers, would be desirable for use in the genetic manipulation of plants.
Reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in any country.